The present invention relates to a chamber for the vapor-phase chemical processing of semiconductor substrates. More particularly, the present invention provides a continuous processing chamber that allows the deposition of highly uniform films with decreased depletion effects.
Vapor-phase processing techniques that utilize the flow of a reactive gas through a processing chamber are central to the ability to fabricate integrated circuits on semiconductor substrates. As an example, chemical vapor deposition (CVD) is one of the most important methods of forming films of SiO2, polycrystalline silicon and silicon nitride on silicon substrates. Other vapor-phase processing techniques, such as dry etching, are equally important.
Chemical vapor deposition is the deposition of a non-volatile film on the surface of a substrate by the reaction of vapor phase chemicals that contain the desired constituents of the product film. Many different types of CVD reactors are known, and may have very different designs and performance characteristics relative to one another. For example, two very broad classes of CVD reactors are atmospheric pressure reactors (APCVD) and low-pressure reactors (LPCVD). Found within each of these classes are both batch process systems, in which wafers are processed one batch at a time, and continuous-process systems, in which wafers are continuously fed through a process chamber while the chamber is maintained at process conditions.
Continuous process chambers are generally preferred over batch process chambers for CVD processes, as the continuous-process chambers generally have a higher throughput, especially for APCVD. Many different types of continuous-process reaction chamber designs are known. For example, some chambers are designed to cause the reactant gas mixture to flow parallel to the wafer surfaces as the wafers move through the chamber. In other chamber designs, the reactant gas initially flows generally perpendicular to the wafer surface, and is then exhausted out of an end of the chamber. Various examples of continuous processing chambers are found in U.S. Pat. Nos. 3,598,082, 3,652,444, 3,750,620 and 5,863,338, the disclosures of which are hereby incorporated by reference.
In spite of the large number of continuous-process CVD reactor designs and the mature state of the technology, many reactors, both APCVD and LPCVD, share some common problems. For example, wafers processed in many CVD chambers may suffer depletion effects. Depletion effects are variations in the thickness (or other properties) of a film due to the depletion of reactant gasses in the reactant gas mixture as the mixture flows through the chamber. In the absence of corrective procedures, thinner films tend to grow on wafers positioned toward the end of the gas flow path than on wafers positioned toward the beginning of the gas flow path.
Several techniques currently exist for ameliorating depletion effects in CVD systems. For example, one common technique is the use of a temperature gradient across the length of a CVD reaction chamber to increase the film deposition rate toward the end of the chamber. Another is the use of a tapered chamber shape that narrows toward the end of the gas flow path, causing reactant gasses to flow more quickly across the wafers positioned in this part of the chamber. Furthermore, the wafer carriers may be rotated during their passage through the deposition wafer to lessen edge-to-edge depletion effects. While these techniques lessen the severity of depletion effects, they may still produce wafers with some degree of non-uniformity.
The present invention provides a processing system for processing a wafer with a processing vapor. The processing system comprises a chamber, a wafer holder disposed within the chamber for holding the wafer, a drive mechanism for moving the wafer holder through the chamber, and a processing vapor inlet disposed within the chamber for introducing the processing vapor into the chamber and directing the processing vapor onto the wafer. The processing vapor inlet has a generally elongate cross-section configured to create a flow of processing vapor with a generally elongate cross-section and to direct the flow onto the wafer surface in an orientation generally perpendicular to the wafer surface, thus causing the formation of a generally linear stagnation zone in the flow of the processing vapor where the flow meets the wafer surface. The processing system may include a first outlet positioned toward the front of the chamber and a second outlet positioned toward the back of the chamber.